Over twenty percent of HIV-positive persons in the United States are unaware of their infection, leading the Institute of Medicine to recently urge further work to compare the effectiveness of HIV screening strategies. This study will use a randomized trial to compare several variants of emergency-room-based HIV-testing policies in order to determine how HIV test acceptance rates can be increased. The testing policies will be designed using principles from behavioral economics, varying the choice architecture and offering small monetary incentives. This will be the first study to measure differences in take-up rates across a variety of promising but largely untested approaches within a unified randomized trial. Three defaults will be tested: traditional opt-in (test only those patients who request testing), opt-out (routinely testing unless patients decline), and active-choice testing (patients are required to state whether they want to be tested). The study will also be the first to test the effect of small monetary incentives ($1, $5, $10) on test take-up. An additional novel study contribution will be to test the hypothesis that compliance with large requests (accept an HIV test) increases after making a small request or pre-commitment - this "foot in the door" technique has not been previously studied in this setting. The factorial design will permit a direct comparison of all interventions, as well as interactions. The study will contribute a nuanced empirical understanding of how testing protocols from behavioral economics theory affect the effectiveness and efficiency of screening programs in an actual scaled-up setting (San Francisco General Hospital). This will assist in implementing and assessing recent CDC guidelines on HIV screening, while also more generally advancing scientific knowledge related to applying behavioral economics in comparative effectiveness research. PUBLIC HEALTH RELEVANCE: The proposed study will investigate how the effectiveness and efficiency of health screening programs can be enhanced by applying recent advances in behavioral economics theory regarding choice architecture and incentives. In particular, we test the extent to which default choices, small incentives, and encouragement methods can increase the currently low rates of HIV testing in many clinical settings such as emergency rooms. CDC guidelines have now embraced the use of opt-out HIV screening, but more nuanced understanding is essential in order to effectively implement such guidelines.